Non-pneumatic flexible wheels or tyres are well known to a person skilled in the art. They have been described in a great number of patent documents, for example in patents or patent applications EP 1 242 254 (or U.S. Pat. No. 6,769,465), EP 1 359 028 (or U.S. Pat. No. 6,994,135), EP 1 242 254 (or U.S. Pat. No. 6,769,465), U.S. Pat. No. 7,201,194, WO 00/37269 (or U.S. Pat. No. 6,640,859), WO 20071085414.
Such non-pneumatic tyres, when they are associated with any rigid mechanical element intended to provide the connection between the flexible tyre and the hub of a wheel, replace the assembly constituted by the pneumatic tyre, the rim and the disc such as are known on most current road vehicles.
In particular, the aforementioned U.S. Pat. No. 7,201,194 describes a non-pneumatic, structurally supported (without internal pressure) tyre, which has the main feature of including a reinforced annular band that supports the load on the tyre and a plurality of support elements or spokes, having very low stiffness in compression, which operate in tension to transmit the forces between the annular band and the wheel hub.
This annular band (or shear band) comprises two membranes, formed from essentially inextensible cords that are coated with natural or synthetic rubber, which membranes are separated by a shear layer that is itself made of rubber. The operating principle of such a band is that the shear modulus of the shear layer is very substantially lower than the tensile modulus of the two membranes, while being sufficient to be able to correctly transmit the forces from one membrane to the other and to thus make said band work in shear mode.
By virtue of this annular band, it is possible to manufacture non-pneumatic wheels or tyres capable of running in severe or harsh conditions without any risk of puncture and without the drawback of having to maintain an air pressure inside the tyre.
Moreover, compared with the non-pneumatic tyres of the prior art, a ground contact pressure which is more uniformly distributed, hence better working of the tyre, an improved road holding and improved wear resistance are obtained here.
However, such a rubber shear band is not without drawbacks.
Firstly, at the customary operating temperatures, for example between −30° C. and +40° C., it is relatively hysteretic, that is to say that some of the energy supplied for rolling is dissipated (lost) in the form of heat. Next, for significantly lower operating temperatures, such as those that can be found, for example in geographical areas of polar type, typically below −50° C. or even less, it is well known that rubber rapidly becomes brittle, frangible and therefore unusable. Under such extreme conditions, it is moreover understood that temperature fluctuations that are more or less sizable and rapid, combined, for example, with relatively high mechanical stresses, could also lead to adhesion problems between the two membranes and the shear layer, with a risk of localized buckling of the shear band level with the membranes and endurance that is in the end degraded.